Audible (s AMZN), the digital audiobook site owned by Amazon that launched audiobook rights platform ACX in 2011 as a way for authors and publishers to profit from their unsold audiobook rights, is now lowering the royalties it pays on those audiobooks.

ACX enables rights holders — authors or publishers, though the site has become increasingly geared toward self-published authors — post their rights on the platform and let producers and narrators bid on them. Once the book is recorded, the rights holder can sell it through Amazon and Audible exclusively for a higher royalty rate, or sell it wherever they want for a lower royalty.

Until now, these royalties have been pretty generous: Creators who agreed to sell exclusively through Amazon and Audible got a rate of 50 to 90 percent, depending on the number of units sold, while creators who chose the non-exclusive option got a royalty…